Studies showing an increased dangerousness of the Delta variant are increasing. According to the latest, published Friday, August 27 in the journal The Lancet Infectious Diseases, the hospitalization rate of people infected with the Delta variant would be doubled compared to infection with the Alpha strain. The Delta variant is a mutated form of SARS-CoV-2, first detected in India in October 2020. Much more contagious than its predecessor, it has become the dominant form of the virus worldwide. In France, on August 3, it represented 98.1% of Covid-19 cases, according to Public Health France.
While there is no doubt about the increased contagiousness of the Delta variant, its degree of virulence – its harmfulness – is however still debated. For this study, teams from the University of Cambridge analyzed data from 43,338 people who tested positive for Covid-19, in the United Kingdom, between March 29 and May 23, 2021. Vaccination status, age and other demographic factors as well as hospital admissions were screened for analysis. There were 51.1% women and 48.9% men; 30% were under 20 years old; 54.6% were between 20 and 50 years old and only 6.2% over 60 years old.
“A probable increased risk linked to the variant”
The authors identified 34,656 cases of the Alpha variant (80% of the patients), the majority in the United Kingdom at the start of the study, and 8,682 cases of the Delta variant (20% of the patients). But the latter’s proportion steadily increased during the follow-up period, reaching 65% in the last week.
The hospitalization rate gives a good idea of the virulence of the coronavirus: it is the severity of the disease that conditions admission to hospital. A total of 2.2% of people infected with the Alpha variant had to be hospitalized (764 people, out of a total of 34,656) within two weeks of their positive test, compared with 2.3% of people infected with the Delta variant (196 people, out of a total of 8,682). But the two groups were not strictly comparable: those infected with the Delta variant were younger, lived in poorer neighborhoods and more often belonged to an Indian ethnicity. To compare them, the authors had to perform a sophisticated statistical analysis (called “stratified Cox regression”), “Necessary and well conducted”, greets Mircea Sofonea, lecturer in epidemiology at the University of Montpellier. Result: the Delta variant multiplies by 2.26 the risk of hospitalization compared to its cousin Alpha.
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